The freezing point is the maximum temperature occurring during the solidification of a super-cooled liquid.
Place a quantity of the substance under examination in the inner tube such that the thermometer bulb is well covered and determine the approximate freezing point by cooling rapidly.
Place the inner tube in a bath about 5° above the approximate freezing point until all but the last traces of crystals are melted. Fill the beaker with water or a saturated solution of sodium chloride at a temperature about 5° lower than the approximate freezing point, assemble the apparatus, ensuring that some seed crystals are present, and stir thoroughly until solidification takes place. The highest temperature observed during solidification of the substance is regarded as the freezing point of the substance.
Apparatus
The apparatus and its dimensions are as shown in the figure.Method
Place a quantity of the substance under examination in the inner tube such that the thermometer bulb is well covered and determine the approximate freezing point by cooling rapidly.Place the inner tube in a bath about 5° above the approximate freezing point until all but the last traces of crystals are melted. Fill the beaker with water or a saturated solution of sodium chloride at a temperature about 5° lower than the approximate freezing point, assemble the apparatus, ensuring that some seed crystals are present, and stir thoroughly until solidification takes place. The highest temperature observed during solidification of the substance is regarded as the freezing point of the substance.
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